In this post we will evaluate what BMI is, its significance and how it determines your nutrition status.
Body Mass Index (BMI ) is derived from anthropometric measurements of nutrition assessment. It requires both the height and weight measurements for it to be calculated. The formula to calculate it is as follows:
Weight (kgs) divide by Height (m2)
Example 1:
Person A is 85kgs and has a height of 6.1 feet.
(i.) You first convert the height into metres by multiplying 6.1 feet by 0.3048 :
6.1 ft × 0.3048 m=1.86 m
If the weight is in pounds or grams, you convert to kgs.
(ii.) You square the metres:
1.86m × 1.86 m
=3.4596 m2
(iii.) Then divide weight in kgs by the height in m2.
85 kgs/3.4596m2
=24.57 kg/m2
So, this person’s BMI is 24.57 kg/m2
Example 2:
Person B has the same kgs but a different height of 5.6 feet.
The steps are similar in that you first convert the feet into metres:
(i.) 5.6 ft × 0.3048 m
=1.71 m
(ii.) Then you square the metres:
1.71 m × 1.71 m
=2.9 m2
(iii.) Then divide weight by the height as follows:
85 kgs/ 2.9 m2
BMI=29.31 kg/m2
BMI scores and how to interpret them:
- Underweight < 18.5kg/m2
- Normal weight 18.5kg/m2 – 24.9kg/m2
- Overweight 25.0kg/m2 – 29.9kg/m2
- Obesity 30.0 kg/m2– 39.9kg/m2
- Extreme obesity >40 kg/m2
You notice that the two individuals have the same height , different weights and thus different BMI. Person A is of normal weight, while person B is overweight.
Adults with BMI of less than 18.5 kg/m2 are considered as underweight; however, the case is different for older adults (>65 years) as a BMI of less than 23 kg/m2 is regarded a lower than recommended weight range.
BMI is an effective tool to determine your nutrition status though it is consistently recommended that any tool utilized for nutrition assessment be combined with one or more other tools to enhance the reliability and accuracy of results. Certainly, there are cases when BMI is not very accurate. For instance, it is possible that certain persons, especially body-builders or individuals with dense bones and muscles have higher BMI levels, exceeding the normal range because the muscles or bones contribute to the heavier mass, in turn higher BMI.
In our next posts , we will look into other nutrition assessment methods in more detail.